Innovative partial hand system

VINCENT partial

  • Modular Design
  • Leight-weight & compact
  • Numerous grip patterns
  • Simple Usage
  • A complete solution
  • Individually adaptable

A partial hand amputation presents a particular challenge for the orthopaedic technician with regard to functional prosthetic restoration. Anatomy and residual function of the partial hand differ to a high degree. For the first time, a new generation of prostheses is enabling the functional replacement of single fingers and the thumb with active electrically driven prosthetic fingers corresponding in size to the anatomy of the human hand.

Restorative treatment following a partial hand amputation can vary greatly and requires highly individual and variable prosthetic solutions. The spectrum ranges from missing individual finger phalanges to entire sections of the metacarpus and the thumb. The situation is potentially complicated further by stiffening of joints, scars and folds in the skin, and the associated functional impairments, as well as hypersensitivity in the remaining sections of the hand. Alongside a sophisticated shaft design, the prosthetic components must satisfy this set of requirements.

Design & Setup

The new partial hand system design aims to enable as far as possible the anatomically and biomechanically correct restoration of the active gripping and holding function. Cosmetic aspects, weight, holding force, gripping speed and noise generation were further aspects considered during this new development. At the heart of the system being presented is an electrically driven single finger prosthesis. It consists of an active prosthesis powered by an electric motor and gearbox integrated into the middle finger. The fingers can also be returned to its original position even when no voltage is applied and is protected against overload by a mechanical overload coupling.

The precise positioning, alignment and connection of the powered finger to the prosthesis shaft without the use of additional aids is time-consuming and complicated. A sturdy aluminium frame assumes positioning, stabilisation and electrical contact of the single finger in series or along a curve, allowing for a slight abduction of the finger at a pre-set angle. The frame may also contain parts of the electronic control unit and sensors.

Thumb active & passive

The thumb is of paramount importance in grasping and holding using the cylindrical or lateral grips as well as with regard to assuming an opposition position to the fingers especially for the precision grips: the pincer grip and the three-point grip. In contrast to the fingers, the loss of the thumb cannot be compensated by the remaining fingers; a significant functional impairment is the result.

Passive Thumb

With regard to restoration in situations in which a thumb stump is insufficiently long or mobile or is lacking other adaptation options for functioning cosmetic treatment of the thumb, a mechanically operated thumb can be a solution. The thumb is equipped with two movement axes. One axis allows the thumb to rotate inwards and outwards, whereby the motion resistance can be set steplessly via a tensioning screw directly on the axis. The second axis features a ratchet-type mechanism. This permits stepless adduction and movement in the opposite direction is prevented by the interlocking teeth. Opening of the thumb is by tensile force at the distal end of the thumb and simultaneous reverse rotational movement.

Active Thumb

In situations where treatment involves the use of powered fingers and the necessary peripherals such as control unit, sensors and battery system are implemented, it can be advantageous to also actively control the thumb, if added functionality for the patient can be achieved as a result. The construction of the proximal passive joint of the thumb is almost identical to that of the manual thumb. The distal powered thumb joint is constructed in a similar way to a single finger, but without a moveable fingertip. Instead, the thumb is sheathed in an elastic PU covering.

System

A number of different components must be integrated in the prosthesis shaft in order to operate the prosthetic finger. The control unit has six slots for four active prosthetic fingers and one thumb with up to two active movement axes, a slot for the vibration motor of the force feedback system and two ports for various sensors. The power supply is connected via an additional slot. Prismatic LiPo cells are generally used in this case. The accumulator cells are charged via a magnetic contact charger, on which the system’s on-off switch is also located. The electronic control is connected via Bluetooth connection to a tablet PC in order to enter patient-specific settings with an app.

Sensors

Control of the prosthesis is either by one or two sensors. The user may choose between EMG sensors, touchpads and bend sensors, whereby a combination of sensors can also be used. If these options are not sufficient, the system can be extended considerably by the addition of further input devices via the Bluetooth module integrated in the 6-channel control unit.

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